The present invention generally relates to ball-point pens, and more particularly to the balls for ball-point pens.
In Japanese Patent Publication No. 31049/1975, a ball for a ball-point pen is disclosed which comprises cemented carbide, e.g., WCxe2x80x94Cr3C2xe2x80x94Co. Such cemented carbide xe2x80x9cballsxe2x80x9d are well known in the writing implement arts, and often have a diameter in the range of 0.3-1.0 mm. Tables 1 and 2 show typical characteristics of known balls next to typical characteristics of balls formed according to the invention, having compositions, hardness, and mean diameter of WC particles for satisfying such design requirements as wear resistance, corrosion resistance to ink, and xe2x80x9cwetting relationshipxe2x80x9d between the ink and the ball, referred to as xe2x80x9cspreadabilityxe2x80x9d of the ink. To put it correctly, conventional examples in Tables 1 and 2, represent characteristics of balls intended for use with oil base ink and water base ink, respectively.
The use of inks consisting of high viscosity gel that is capable of fully dispersing heavy and hard inorganic pigments (e.g., titania and zinc white, etc.) is increasing. When conventional balls, of the types characterized in Tables 1 and 2, are used with gel ink of a high viscosity and comprising hard inorganic pigments, portions exposed on the ball surface of the Cr3C2xe2x80x94Co phase (which is a binder of the WC particles) are worn severely. In many cases, as a result of this severe wear, the WC particles drop out of their locations on the surface of the ball. These loose WC particles tend to act as an abrasive or polisher. As a result, the main body of the pen-point is often significantly worn down by the abrasive action of these loose WC particles. Consequently, the ball sinks into the main body of pen-point, giving rise to the following problems:
(1) ink does not flow out easily as the ink grooves formed in the main body of the pen-point are blocked;
(2) frictional resistance increases as the contact area between the ball and the main body of the pen-point increases, thereby making it difficult for the ball to roll properly; and
(3) unless the ball-point pen is utilized in a substantially upright position, the ball holding section of the main body of the pen-point engages the paper, causing the pen-point to be scratchy, i.e., the angle between the paper and the ball-point pen which allows writing without causing the pen-point to be scratchy becomes larger. Moreover, as the angle becomes larger, it becomes increasingly difficult for the ink to be dispensed from the pen-point.
The above-mentioned problems result in the writing performance of the ball-point pen worsening at an early stage, because the main body of pen-point wears out quickly. This is particularly true with the conventional balls characterized in Tables 1 and 2.
In addition, the mean diameter of the WC particles exposed on the surface of the ball is relatively large in the conventional balls characterized in Table 2. Here, the surface area of the CrSC2xe2x80x94CO phase, which controls the xe2x80x9cspreadabilityxe2x80x9d of the ink, is relatively small. This results in poor xe2x80x9cspreadabilityxe2x80x9d of the ink, causing the written lines to be broken or uneven. This poor performance is increased when such prior art balls are used in combination with high viscosity gel inks containing heavy and hard inorganic pigments.
The present invention solves these and other problems in the art by providing a ball for a ball-point pen which is capable of reducing wear on the main body of the pen-point of a conventional ball-point pen thereby maintaining good writing performance for a longer term, even if high viscosity gel inks with heavy and hard inorganic pigments are employed. The present invention provides a ball for a ball-point pen comprising cemented carbide of WCxe2x80x94Cr3C2xe2x80x94Co wherein VC exists as solid solution in the Cr3C2xe2x80x94Co phase which is a binder of WC particles and the mean diameter of the WC particles is in the range of from about 0.3 to about 0.5 xcexcm. In a preferred embodiment of the invention, the surface of the ball which includes a portion of the Cr3C2xe2x80x94VCxe2x80x94Co phase is formed so as to include a plurality of concave recesses.
A ball formed in accordance with the preferred embodiments of the invention will at least include characteristics such as:
(1) hardness increases, because the WC particles are bonded in a more xe2x80x9cdensexe2x80x9d state than with prior art ballpoint pen balls; and therefore wear and abrasion resistance improves;
(2) the mean diameter of the WC particles exposed on the surface of the ball is smaller than that of the prior art, with the surface area of the Cr3C2xe2x80x94VCxe2x80x94Co phase being greater, therefore, even if high viscosity gel inks including heavy and hard inorganic pigments are used, the following effects may be achieved:
(a) the WC particles will not drop out easily. Moreover, even if the particles drop out of the ball, the wear on the main body of pen-point will be reduced, because the mean diameter of the particles is relatively small; and
(b) the xe2x80x9cspreadabilityxe2x80x9d of the ink is significantly improved such that the written line will not get broken or uneven.
In addition, since a portion of the exposed surface of the ball having a Cr3C2xe2x80x94VCxe2x80x94Co phase is concavely formed, the writing performance is improved because the ball will roll with the ink maintained within the plurality of concave recesses formed on the surface of the ball.